Grinding wheel is a widely used cutting tool to remove undesired material from work piece by abrasive action. Industrial applications of grinding wheels are: cylindrical grinding, profile grinding, internal grinding, honing and super-finishing, centreless grinding, surface grinding etc. The grinding wheels are typically used in various industries including bearing industries, automobile, defense, foundries, forging industries, steel plants, and machine/cutting tool manufacturing, structural fabrication, etc. Generally, the grinding wheels are used in the entire engineering industry. Efficient grinding wheels should have a high and constant cutting capacity and excellent profile durability.
In the manufacturing of grinding products such as resinoid grinding wheels, which are designed to perform heavy duty tasks such as metal cutting made with an abrasive material which is intimately mixed with the bonding ingredients and temporary binders. The bonding ingredient consists of such compounds as are necessary to combine to form the required resinoid bond during curing. The ingredients are mixed and pressed into the required shape. The green product (green grinding wheel) thus obtained, is then placed in the oven for curing for several hours in order to achieve a slow heating to avoid any damage to the product. Typically in the conventional process, green grinding wheels are cured for several hours ranging from 15-30 hours using radiant heating in electrical or gas fired or oil fired ovens at about 180-220° C. with several intermediate holds at different temperatures, by using radiant heating. During the conventional process of curing, pressure is also employed by inserting metallic plates between the green samples.
The conventional process of curing green grinding wheels requires longer duration heating for achieving desired bond strength between ceramic grains and phenolic resins, as both are bad conductors of heat. This results in spending considerable time and energy to achieve the desired properties.
Thus, there is a need to improve the prior art, by lowering the time and energy required during the conventional process of curing of green grinding wheels.
Prior art teaches various techniques used to lower such time and energy in the process of manufacture of grinding wheels, with the help of use of electromagnetic radiations such as microwave. Examples can be seen as follows:    1) U.S. Pat. No. 5,072,087 claims a process of producing a heat-treated body from a material preferably dielectric ceramic that does not couple well with microwaves at room temperature. However, the invention uses microwave susceptors made from similar material which couples well with microwaves at room temperature and gets converted to substantially the same as the sample material during the microwave heating step. This is done to avoid contamination of the final product.    2) U.S. Pat. No. 4,305,898 discloses a method for the manufacture of a bonded abrasive grinding product using microwave system. The said patent uses a steel or other metallic reinforcing ring in a grinding wheel without it being damaged or destroyed during heating. This process is used only for the manufacturing of swing frame & pedestal grinding wheels where maintaining of profile is not critical as they are flat wheels. Using this process, only a flat and thick swing frame & pedestal wheel can be processed in a single layer only. The limitation of this process is it cannot maintain the critical and complex profile of the wheel after processing and cannot cure grinding wheels in multiple stacking for better economics.    3) U.S. Pat. Nos. 4,150,514 and 4,404,003 disclosed the process in which the mixture was prepared by blending of refractory particles, binder and filler. This mixture was subjected to microwave energy at about 2.45 GHz. This heats the charge to a temperature within the range of about 35-120° C. This is called the preheating process of the grinding wheel mix. Then this preheated mix was transferred to molds which were then placed between the platens of a hot mold press and mold was subjected to pre-curing heating step in accordance with conventional procedures. The curing is done using electrical resistance heating or oil firing or gas firing as per desired time temperature profiles. These patents used the microwave only for the preheating of the mixture which provides fluidization and minimizes the degree of pressure required for the production of any given density of resin-abrasive mixture. The final curing of the grinding wheel was followed by the conventional route.
However, as seen above, these techniques have some limitations in spite of using microwave heating for curing and there is further scope of conserving time and energy.
It is an object of the present invention to carry out the process of curing of green grinding wheels in significantly shortened time period using microwave energy, and consequent reduction in energy consumption.
In the conventional process where curing is done using electrical resistance heating or oil firing or gas firing, a steel plate weighing nearly about 1000 g is used for the curing of single sample each weighing about 90 g to retain the geometry of the samples. This creates nothing but excessive dead load. During the conventional heating process, unnecessary heating of the steel plate and side walls of the furnace/oven also consume disproportionate energy.
The use of such metallic plates during microwave heating may cause reflections of microwaves from the metal plates which may tend to damage the magnetron and there is fear of forming hot spots in the microwave cavity. Therefore, there would be an increased risk of damage to be caused to the magnetron and microwave chamber internally. It would also result in uneven heating of the sample and waste of energy due to reflections.
Thus it is seen that there is a need to improve the prior art by reducing unnecessary and wasteful dead load used in the conventional process of curing and also save the energy wasted in heating the same.
It is clear that a plain substitution of microwave process to the conventional heating process is not the solution to the limitations posed by the prior art.
Further, the sample to be cured needs to be evenly heated with a uniform temperature all over its body for retaining its shape.
The shape of the sample to be cured should not be affected while curing, due to uneven weight load or due to uneven heating.
Thus, there is a need to devise a system for rapid and uniform curing of grinding wheels which steers away from the limitations noted above, and achieves the intended objects.